Molybdenum(II) acetate is a
coordination compound
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...
with the formula Mo
2(O
2CCH
3)
4. It is a yellow,
diamagnetic
Diamagnetic materials are repelled by a magnetic field; an applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. In contrast, paramagnetic and ferromagnetic materials are attracted ...
, air-stable solid that is slightly soluble in organic solvents. Molybdenum(II) acetate is an iconic example of a compound with a metal-metal
quadruple bond
A quadruple bond is a type of chemical bond between two atoms involving eight electrons. This bond is an extension of the more familiar types double bonds and triple bonds. Stable quadruple bonds are most common among the transition metals in the m ...
.
[Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J., "Synthesis and Technique in Inorganic Chemistry third edition", University Science Books: Mill Valley, CA, 1999, ]
Structure and bonding
It adopts the same
Chinese lantern structure
In chemistry, the Chinese lantern structure is a coordination complex where two metal atoms are bridged by four bidentate ligands. This structure type is also known as a paddlewheel complex. Examples include chromium(II) acetate, molybdenum(II) ...
as related acetate dimers such as
rhodium(II) acetate
Rhodium(II) acetate is the coordination compound with the formula Rh2(AcO)4, where AcO− is the acetate ion (). This dark green powder is slightly soluble in polar solvents, including water. It is used as a catalyst for cyclopropanation of a ...
,
copper(II) acetate
Copper(II) acetate, also referred to as cupric acetate, is the chemical compound with the formula Cu(OAc)2 where AcO− is acetate (). The hydrated derivative, Cu2(OAc)4(H2O)2, which contains one molecule of water for each copper atom, is avail ...
, and
chromium(II) acetate
Chromium(II) acetate hydrate, also known as chromous acetate, is the coordination compound with the formula Cr2(CH3CO2)4(H2O)2. This formula is commonly abbreviated Cr2(OAc)4(H2O)2. This red-coloured compound features a quadruple bond. The prepara ...
. Each Mo(II) center in Mo
2(O
2CCH
3)
4 has four d
valence electrons
In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed. In a single covalent bond, a shared pair forms ...
. These eight d-electrons form one
σ, two
π bonds
In chemistry, pi bonds (π bonds) are covalent bond, covalent chemical chemical bond, bonds, in each of which two lobes of an atomic orbital, orbital on one atom overlap with two lobes of an orbital on another atom, and in which this overlap oc ...
, and one
δ bond, creating a bonding
electron configuration
In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom ...
of σ
2π
4δ
2. Each of these bonds are formed by the overlapping of pairs of d orbitals.
[Blaudeau, J. P.; Pitzer, R. M. “ Ab Initio Studies of Ligand Effects on the Metal-Metal Bond in Dimolybdenum Complexes” J.Phys. Chem. 1994, vol. 98, pp. 4575-4579.] The four acetate groups bridge the two metal centers. The Mo-O bond between each Mo(II) center and O atom from acetate has a
distance
Distance is a numerical or occasionally qualitative measurement of how far apart objects or points are. In physics or everyday usage, distance may refer to a physical length or an estimation based on other criteria (e.g. "two counties over"). ...
of 2.119 Å, and the Mo-Mo distance between the two metal centers is 2.0934 Å.
Preparation
Mo
2(O
2CCH
3)
4is prepared by treating
molybdenum hexacarbonyl
Molybdenum hexacarbonyl (also called molybdenum carbonyl) is the chemical compound with the formula Mo(CO)6. This colorless solid, like its chromium and tungsten analogues, is noteworthy as a volatile, air-stable derivative of a metal in its zero ...
(Mo(CO)
6) with
acetic acid
Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
. The process strips
CO ligand
In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electr ...
s from the hexacarbonyl and results in the oxidation of Mo(0) to Mo(II).
[Brignole, A.G.; Cotton, F.A., “Rhenium and Molybdenum compounds containing quadruple compounds” Inorg. Synth. 1972, volume 13, pp. 81-89. ][Pence, L. E.; Weisgerber, A. M.; Maounis, F.A.; “Synthesis of Molybdenum-Molybdenum Quadruple Bonds” J. Chem. Educ., 1999, vol. 76, 404-405.]
:2 Mo(CO)
6 + 4 HO
2CCH
3 → Mo
2(O
2CCH
3)
4 + 12 CO + 2 H
2
Trinuclear clusters are byproducts.
The reaction of HO
2CCH
3 and Mo(CO)
6 was first investigated by Bannister et al. in 1960. At the time, quadruple metal-metal bonds had not yet been discovered, so these authors proposed that Mo(O
2CCH
3)
2 was tetrahedral.
[Bannister, E.; Wikinson, G. “Molybdenum(II) carboxylates” Chem. Ind. 1960, 319.][Stephenson, T.A.; Bannister, E.; Wilkinson, G. “Molybdenum(II) Carboxylates” J. Chem. Soc., 1964, pp. 2538. ] This perspective changed with Mason's characterization.
Applications
Mo
2(O
2CCH
3)
4 is generally used as an intermediate compound in a process to form other quadruply bonded molybdenum compounds.
The acetate ligands can be replaced to give new compounds such as
o2Cl8sup>4− and Mo
2Cl
4 (C4H9)3sub>4.
[Tsai, Y.C.; Chen H.Z.; Chang, C.C.; Yu, J.K.; Lee, G.H.; Wang, Y.; Kuo, T.S. “Journey from Mo-Mo Quadruple Bonds to Quintuple Bonds” J. Am. Chem. Soc.,2009, 131, 12534-12535. ][Handa, M.; Mikuriya, M.; Kotera, T.; Yamada, K.; Nakso, T.; Matsumoto, H.; Kasuga, K. “Linear Chain Compounds of Molybdenum(II) Acetate Linked by Pyazine, 4,4’-Bipyridine, and 1,4- Diazabicyclo .2.2ctane” Bull. Chem. Soc. Jpn., 1995,68, 2567-2572.]
References
{{DEFAULTSORT:Molybdenum(Ii) Acetate
Acetates
Molybdenum(II) compounds